Since the past, nitrile rubber (acrylonitrile-butadiene copolymer rubber) has been used as a material for rubber parts such as hoses, belts, and tubes for automobiles by taking advantage of its oil resistance, mechanical properties, chemical stability, etc. Further, highly saturated nitrile rubber obtained by saturation by hydrogenating the carbon-carbon double bonds in the polymer main chain of the nitrile rubber is further excellent in heat resistance, so is being used for rubber parts such as seals, belts, hoses, and gaskets.
On the other hand, while art relating mainly to styrene-butadiene rubber, Patent Document 1 discloses the method of drying an aqueous dispersion containing a latex of styrene-butadiene rubber and a staple fiber having an average diameter of less than 0.5 μm to produce a rubber/staple fiber master batch. In this Patent Document 1, the above method of production is used to improve the abrasion resistance, fatigue resistance, etc. However, the cross-linked rubber obtained by the art of Patent Document 1 is not sufficient in heat resistance, in particular, tensile strength at a high temperature, and therefore is not suitable for use for applications where use at a high temperature is envisioned such as the above-mentioned seals, belts, hoses, and gaskets.